Probiotics have been shown to have beneficial effect on the growth performance of newborn animals. However, the results are inconsistent, especially in Iran. A meta-analysis was carried out to evaluate the effects of probiotics on dry matter intake (DMI), daily weight gain (DWG) and feed efficiency (FE) in suckling calves using data from the studies conducted in Iran. The literature review resulted in 13 documents including 6 and 5 papers written in English and Farsi respectively, as well as 2 papers presented in national conferences. Random effect meta-analysis was performed to evaluate the effect of probiotics on growth performance of the suckling calves using STATA statistical software on 8 papers that were identified as suitable for the objective of this study. Univariate and multivariate meta-regression analyses were also performed to evaluate the effects of experimental period (≤8 weeks vs. >8 weeks), gender of calf (male vs. female), type of probiotic (bacteria vs. a combination of yeast and bacteria), and probiotic administration manner (in milk vs. in starter) on the study outcomes. The results of meta-analysis showed no significant effect of probiotics on DMI. However, a significant difference was identified by subgroup meta-analysis between the experimental period subgroups for the effect of probiotics on DMI. Probiotics administration increased DWG of suckling calves by 47 g/day (P<0.01). The effect of probiotics on feed efficiency was not significant. The results indicated that the probiotic administration may improve DMI and DWG in suckling calves.
